Fuse links



J. FEENAN ET AL FUSE LINKS Filed March 29. 1968 Aug. 4, 1970 FIG.2

FUSE LINKS John Feenan, Ronald Vincent Wafer, and Eric Jacks, Liverpool, England, assignors to The English Electric Company Limited, London, England, a British coman p y Filed Mar. 29, 1968, Ser. No. 717,246 Claims priority, application Great Britain, Mar. 30, 1967,

14,466/ 67 Int. Cl. H01h 85/12, 85/30 U.S. Cl. 337-161 3 Claims ABSTRACT OF THE DISCLOSURE This invention relates to fuse links.

From one aspect, the present invention consists in a fuse link comprising a tubular body of insulating material having conductive caps on its ends, a plurality of elongated fusible elements extending along radial planes and connected between the said caps, the elements being equidistantly spaced from one another and each comprising strip material so shaped in cross-section as to be `selfsupporting along its length.

The elements may all lie along a single circle concentric with the axis of the fuse link, the relative disposition of the elements being determined by plates pierced to locate and support them as desired, and a spring-actuated trip indicator may be provided to give an indicationof the elements having blown.

The invention is of particular utility when applied to high voltage fuses employed for motor protection since the fuse elements have to withstand starting surges during which they may have to carry many times their rated current for short periods, resulting in expansion, and then subsequent contraction, of the elements. Hitherto, the elements have frequently been wound on formers and this repeated expansion and contraction to which the elements are subjected and the resulting relative movement between the elements and the former, has caused the elements to break, whereas, by constructing the elements to be self-supporting in accordance with this invention, the incidence of breakage may be eliminated.

In order that the invention may be fully understood, one embodiment thereof will now be described with reference to the accompanying drawing in which:

FIG. 1 is an axial section along a fuse link according to this invention; and

FIG. 2 is a cross-section along A-A in FIG. l.

Referring now to the drawings, the fuse link comprises an electrically insulating tubular body 3 made from a material possessing arc-inhibiting properties, that is, a material which not only resists the scorching eiect of any arc struck in its vicinity but actually emits fumes which are arc-inhibiting. Examples of such materials suitable for use here will be found in British Patent No. 1,109,860. Secured to the ends of this body are inner conductive plates 4 and 5 which are pierced to accommodate a plurality of elongated fuse elements 6 and locate them in the desired relationship, the exposed ends of the elements being bent over the outside of the plates. These elements are constructed from silver strip and are so shaped in cross-section as to be self-supporting. Further, the elements are pierced along their length at intervals to United States Patent O "Ice give them the desired characteristics under both shortcircuit and overload conditions and they may conveniently be of the form described in our co-pending patent application 717,211 entitled High Voltage Fuse Elements and filed on the same date as this application. The elements are rigidly secured in position by a plain conductive plate 7 at one end which is clamped against the supporting plateS by an end cap 8, and by a dished cap 9 at the other end which is similarly clamped against the supporting plate 4 by an end cap 10.

The dished cap 9 is so formed to accommodate a trip indicator plunger 12 which is secured to a high resistance wire 13, this wire being held in tension between the plate 7 and the plunger under the action of a compression spring 15. Since the wire extends freely through the wall of the cap 9 from within the fuse, and the whole enclosure is filled with an arc-quenching sand, a sealing disc 16 is provided for it, this disc in turn being clamped in position by an inner cap 17. The current-carrying capacity of the trip wire is such that, when the fuse elements blow, the trip wire is ruptured also and the restoring action of the spring urges the plunger into an exposed position.

Although the fuse link has been described above in relation to the accompanying drawing, it is to be understood that various modifications may be made without departing from the scope of this invention. For example, although the disposition of the L-shaped elements shown, withone limb perpendicular to a radial plane, is particularly advantageous since the growth of fulgurite from any one element under operating conditions does not readily merge with that from another, and more eilcient use is made of the available space, the sulf-supporting elements may alternatively be disposed in other relationships with one another. Furthermore, other cross-sectional shapes, c g. any one of those disclosed in the co-pending application referred to, may be employed instead of the L-shape shown, all these elements producing an improved performance over the more conventional elements at both high prospective currents and, more particularly, on the lower overcurrent duty.

We claim:

1. A sand-filled fuse link comprising a tubular body of insulating material,

two pierced conductive end plates, one mounted on each end of the body,

two conductive end caps mounted over the corresponding end plates, one of said caps being mounted over its said end plate through the intermediary of a plain conductive plate and the other one of said caps being mounted over its said end plate through the intermediary of a dished member defining an inwardly extending cavity coaxial with the body,

a spring-biased plunger house in said cavity,

a trip wire extending axially of the fuse link and secured at one end to said plunger and* at the other end to said plain plate, the plunger being projected under the action of the spring bias in response to the rupture of the trip wire, and

a plurality of elongated fusible elements extending along radial planes within the body each comprising strip material so shaped in cross-section as to be selfsupporting along its length, the elements being accommodated by the pierced end plates which determine their disposition equidistantly spaced from one another and concentric with the axis, the ends of the elements being bent outwardly and firmly secured solely between these end plates and the plain plate on the one hand, and the dished member on the other.

2. A fuse link according to claim 1, wherein the elements are L-shaped in cross-section, one limb of each 4 element lying perpendicularly to the radial plane along 2,866,037 12/ 1958 Stewart 337--161 which it extends. 1,927,905 9/ 1933 Slepian et al. 337--159 3. A fuse link according to claim 2, wherein the tubular body is made from a material possessing arc-inhibiting FOREIGN PATENTS properties. l

References Cited 5 807,347 1/1959 Gleat Brltam.

UNITED STATES PATENTS BERNARD A. GILHEANY, Primary Examiner 3,391,369 7/ 1968 Kozacka 337-229 XR D. M. MORGAN, Assistant Examiner 3,183,327 5/1965 Kozacka 337-292 XR 3,147,355 9/1964 Beau 337 229 10 U.S. C1. XR.

3,134,874 5/1964 Cameron 337-158 XR 337-229, 244, 295 

